Stretch array for scanning



May 1, 1962 c. J- SLETTEN STRETCH ARRAY FOR SCANNING Filed D60. 19. 1958 FIG.|

INVENTOR. CAR LYLE J SLETTEN Y B burnt... Mm /f ATTOR/VE X9 United States Patent 3,032,763 S'I'RETCH ARRAY FOR SCANNING Carlyle J. Sletten, Box 185, Acton Center, Mass. Filed Dec. 19, 1958, Ser. No. 781,815 8 Claims. (Cl. 343-793) (Granted under Title 35, U5. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates generally to antennas and more particularly to the production of a scanning action in the type of antenna disclosed in my co-pending application titled Method and Means for Antenna Coupling, application Serial Number 613,011, filed October 1, 1956, now Patent Number 2,963,703.

The electromagnetically coupled radiating elements of the array to be scanned are arranged such that opposite phasing is applied to adjacent elements of the array and the electrical phase between the elements is varied by a physical movement of the elements relative to each other.

Scanning antennas have utility in radar, communication and direction finding applications. Prior art devices for scanning usually involve a physical rotation of the entire antenna or the use of inherently unreliable electronic circuitry. The device of the instant invention utilizes a simple mechanicalmovement which may be operated at high scanning rates with the movement of small masses.

Accordingly, it is an object of this invention to produce a novel scannable antenna.

Another object of this invention involves the production of a novel antenna utilizing electromagnetic coupling to a transmission line.

Still another object of this invention involves the production of a novel scannable antenna which does not introduce any connections to or alterations in the antenna element feeding means.

A further object of this invention involves the scanning of a beam of electromagnetic energy in space wherein the antenna pattern is controlled by electromagnetic coupling of antenna radiating elements.

A still further object of this invention involves the scanning of a beam from an antenna whose radiating elements are excited by their proximity to an open transmission line carrying equal and opposite currents.

It is another object of this invention to produce a novel scannable antenna which utilizes conventional, currently available materials which lend themselves to standard mass production manufacturing techniques.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, wherein:

FIGURE 1 is a pictorial view of an antenna array using electromagnetic coupling of radiating elements to an open transmission line carrying equal and opposite currents with means for mechanically varying the electrical phase between elements along the array;

FIGURE 2 is a plan view of the dipoles in one position and;

FIGURE 3 is a schematic showing of an alternative means for varying the electrical phase.

In accordance with the theory outlined in my aforementioned co-pending application Serial Number 613,001, now Patent No. 2,963,703, the coupling principle upon which this invention is based depends upon the orientation of a radiating element with respect to an open transmission line carrying equal and opposite currents. Although the antenna of this and my co-pending application disclose two-wire line and dipoles, other transmission lines and dipoles, different from that shown in the figures, come within the concept of this invention, for example, a four wire or parallel plate transmission line may be used with curved or other shaped radiating elements.

When a dipole is oriented parallel to the axis of a twowire line, the currents in the line couple equally to the dipole, and there is zero radiation. Rotation of the dipole places alternate segments of the two-wires closer to the dipole such that the currents in the two-wire line electromagnetically couple unequally to the dipole to produce a radiation. When the radiation and coupling characteristics of a single rod on a two-wire line are known, the antenna. performance can be determined by reference to known linear array theory. The coupling of a half-wave rod oriented with respect to a two-wire line depends upon the following parameters:

( 1) The rod length;

(2) The frequency of the electromagnetic waves on the exciting two-wire line;

(3) The spacing of the rod above the two-wire lines;

-(4) The diameter of the two-wire lines;

(5) The spacing between centers of the two-wire lines;

(6) The position of the rods with respect to the twowire line terminations;

(7) The intercoupling between adjacent elements; and

8) The angular rotation of the rod with respect to the axis of the two-wire line.

By utilizing empirically obtained conductance data in conjunction with known linear array theory an antenna may be produced which comprises a balanced two wire line 1011 which feeds approximately A/Z radiating rods or dipoles 12 which are supported on a pair of parallel rails 10-41 constituting a two-wire transmission line as shown in FIGURE 1. No metallic contact or coupling mechanism other than the electromagnetic coupling due to the proximity and orientation of the rod 12 with respect to the two-wire line 10-11 is used. By choosing the angular orientation of the dipoles, almost any total conductance can be obtained in an array. The number of elements that can be fed is limited only by the size of antenna that can be accommodated and the gain requirement. The two-wire lines 1011 may be made heavy enough to support the dipole elements without the need for a plurality of spacer elements along its length. A ground plane 13 beneath the antenna enables the image to improve gain, while light loading and the use of elements 12 in even pairs keeps the amount of unbalance of the two-wire line to a minimum. 0

Scanning of the radiated beam is achieved by utilizing slidable supports 14 for dipoles 12. Rectilinear movement of supports 14 is such that the spacing between centers of the dipoles varies from N2 (FIGURE 2) to a maximum distance of A (FIGURE 1) to cause a variation in the electrical phase between the elements along the array. The spacing between successive dipoles are always proportional.

The particular angular orientation of the radiated beam may be predicted according to SlD. 9g= D x0) where 0 is the angle of the beam from the normal to the array, 1 is the phase velocity factor along the line, D is the center to center spacing between adjacent radiating elements, and A is the Wavelength in free space of the frequency used.

At M2 spacing between the dipoles, the phase shift between elements is due to the plus and minus angles of rotation of dipoles 12. Variation from M2 causes a beam scan in the plane containing the array.

Slidable supports 14 are moved so as to vary the spacing spear ea between array elements 12 such that each dipole is spaced from its adjacent radiating member by the same amount. An elastic material 15 is connected to a fixed support 16 at one end of the array and is clamped to each sliding member 14- at 1'7. The remaining end of elastic member 15 rides on an idler pulley 18 and is driven by a crank operated drum 18a which is operated so as to alternately tension and relax elastic member 15 to cause the variation in distance between dipoles 12. The support means 14, 16, idler pulley 18, and drum 18a are made of dielectric material in order to avoid interference with the radiated beam. To avoid a tendency for support members 14 to overshoot their desired travel distance, an adjustable friction means, such as a non-metallic set screw 19 for example, may be provided to exert a force between line elements -11 and the portions of 14 journalled there- Although one mechanical means has been described for producing the desired variation in electrical phase, it should be understood that any means for tensioning element may be provided or, furthermore, a device such as that shown in FIGURE 3, which will produce the desired motion, may be utilized.

FIGURE 3 schematically shows a lazy tongs type of pantograph 20 which is operated by an eccentric 21 which imparts an oscillatory motion to link '22 which drives piston 23 in guides 24 in a straight line motion. Piston 24 is pivotally attached to one end of the pantograph while the other end is fixed as shown at 28. Since the opening and closing of the pantograph linkage imparts a small vertical motion to the pantograph, pins 25, which are secured in a vertical hole (not shown) in support member 14 for translatory actuation of the dipoles, have slots 26 in which the pins 27 of the pantograph ride. Thus, it can be seen that a variation in electrical phase may be produced between adjacent dipole elements.

Although the invention has been described with reference to particular embodiments, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

I claim:

1. An antenna suitable for scanning a predetermined pattern of energy in space comprising a transmission line permanently fixed in position and in the form of a pair of parallel rails carrying equal and opposite currents, a plurality of radiating elements journalled to and having limited reciprocability along said parallel rails with predetermined couplings caused by the orientation of said radiating elements with respect to the elements of said transmission line, said radiating elements having opposite phasing applied to adjacent radiating elements, and means for moving said radiating elements relatively of said transmission line, and of each other, to vary the electrical phase between said radiating elements while maintaining the said parallel rails in their pre-fixed physical setting.

2. A device as defined in claim 1 wherein said lastmentioned means comprise a cycling mechanism for physically varying distance between said radiating elements while maintaining proportional spacing between successive elements.

3. A device as defined in claim 2 wherein said mechanism for varying the distance between radiating elements comprises elastic means connected between said elements, and means for alternately tensioning and relaxing said elastic means.

4. A device as defined in claim 1 wherein said means for varying the electrical phase comprises'a mechanism for physically varying the distance between said support means and relative to said fixed transmission line while maintaining proportional spacing between said radiating elements.

5. A device as defined in claim 4 wherein said mechanism for varying the distance between radiating elements comprises elastic means connected between said support means, and means for alternately tensioning and relaxing said elastic means at a predetermined periodicity.

6. A device as defined in claim 4 including a ground plane mounted adjacent said transmission line and on a side opposite to the direction of emission of energy from said radiating elements in a manner increasing the gain of said radiating elements.

7. A device as defined in claim 1 wherein said radiating elements are afiixed to supports slidable along said parallel rails without altering the physical characteristics of the transmission line constituted by said parallel rails and wherein said moving means operates to vary the rectilinear spacing between said radiating elements while maintaining proportional spacing between successive radiating elements.

8. An antenna assembly suitable for scanning a predetermined pattern of electromagnetic energy in space comprising feeding means in the form of permanently positioned structure extending the full length of the antenna assembly and carrying equal and opposite currents, a plurality of radiating elements mounted on slidable supports having rectilinear movement relative to said feeding means without introducing any alterations in said feeding means, said radiating elements having a predetermined electromagnetic coupling with said feeding means caused by the orientation of said elements with respect to said feeding means, and cycling means connected with all of said radiating elements for moving said elements relative to said feeding means rectilinearly while maintaining proportional spacing between successive radiating elements, said rectilinear movement varying the electrical phase between said radiating elements causing a beam scan in the plane containing the array.

References Cited in the file of this patent UNITED STATES PATENTS 1,347,440 Callaghan July 20, 1920 2,211,004 Conklin Aug. 13, 1940 2,413,836 Larson Jan. 7, 1947 2,433,369 Kandoian Dec. 30, 1947 2,535,049 De Rosa Dec. 26, 1950 2,605,413 Alvarez July 29, 1952 2,716,703 Kane Aug. 30, 1955 

